Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface showing a first image in a sequence;

FIG. 2 is a second image in a sequence thereof; and,

FIG. 3 is a third image in a sequence thereof.

The broken lines showing the display screen or portion thereof and portions of the graphical user interface form no part of the claimed design.

The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 